Comparable Role in Dust and and Biomass-Burning to Aerosol Optical Depth at a Colorado Mountain-top Site

Abstract:

Visible Multifilter Rotating Shadowband Radiometer (MFRSR) data were collected at Storm Peak Laboratory (SPL), a mountain top facility in northwest Colorado, from 1999-2011 and in 2013. From 2011-2014, in-situ measurements of aerosol light scattering were also obtained. Using these datasets together, the seasonal impact of dust and biomass burning is considered for the western United States. Analysis indicates that the median contributions to spring and summer aerosol optical depth (AOD) from dust and biomass-burning aerosols across the dataset are comparable. The Ångström exponent showed a significant increase in the summer for both the in situ and MFRSR data, indicating an increase in combustion aerosols. Spring dust events are less distinguishable in the in-situ data than the column measurement, suggesting that a significant amount of dust may be found above the elevation of SPL, 3220 m asl. Twenty-two known case studies of intercontinental dust, regional dust, and biomass burning events were investigated. These events were found to follow a similar pattern, in both aerosol loading and Ångström exponent, as the seasonal mean signal in both the MFRSR and ground-based nephelometer. This dataset highlights the wide scale implications of a warmer, drier climate on visibility in the Western U.S.